1. Field
The embodiments disclosed herein are in the technical field of utility grid power regulation. More particularly, the present invention is a potential energy storage ancillary services system for connection to the utility grid and employing electrically powered heavy mass shuttle units on a track system to absorb and provide electrical power from and to the grid.
2. Related Art
The electric power grid is increasingly complex and the matching of power generation supply with power usage is a critical element in maintaining stability in operation. This issue is becoming more complicated with the addition of alternative energy generation sources such as wind power and solar power, which have inherent issues with consistency of power production. As such, transmission system operators and utilities require an increasing amount of ancillary services in order to maintain control and reliability of the electric grid. Based on usage demands, system loading, generation resources, and maintenance requirements, ancillary services provide a means for balancing generation with load as close to instantaneously as possible while also providing a continuous source of reserve power. Ancillary services are comprised primarily of the following components. Regulation is provided by power sources online, on automatic generation control, that can respond rapidly to system operator requests for trimming the minute-to-minute fluctuations in system load (as may be reflected by changes in the grid frequency), by providing either regulation-up (adding power to the grid) or regulation-down (withdrawing power from the grid); Spinning Reserves,—are power sources which are synchronized to the grid and may be brought up to full output within 10 minutes; Supplemental Reserves—offline reserves which may be brought to full capacity online within 10 minutes; Replacement Reserves—offline resources which may restore Spinning and Supplemental Reserves to their pre-contingency status; Black Start—reserve power capacity to re-energize a failed transmission system and VAR Support—the injection or absorption of reactive power (VAR) to maintain grid voltage by synchronizing current to frequency.
In order to provide these ancillary services it is necessary to have a power capacity and an energy reserve. As such, energy storage technologies are ideal suppliers of ancillary services; they have the capacity to respond faster to changing loads than generators and are capable of providing the required functions without the production of fossil fuel emissions.
Ancillary services from energy storage may be provided by battery technologies, capacitors, kinetic energy storage systems such as flywheels or potential energy storage systems such as pumped hydro; however, each technology has disadvantages in its ability to perform the required functions. Battery technologies have a limited cycle life, which is related to the depth of discharge per cycle. This necessitates battery replacement after a limited operating life, which greatly impacts the cost effectiveness of batteries deployed in high cycle ancillary services operations such as Regulation. Conversely, lower cycle rate ancillary services such as Spinning and Supplemental reserves have a greater depth of discharge which also reduces battery life, in all, making batteries an expensive option for ancillary services. Capacitors have very fast response times and potentially high power levels but very limited amounts of energy storage per unit of power; the same holds true for flywheels in which delivery at rated power is typically measured in minutes. By far the most common form of energy storage is pumped hydro. Pumped hydro is a form of potential energy storage in which electricity from the grid is used to pump water from a lower elevation reservoir to a higher elevation; the stored water may then be released through turbines to convert the stored energy into electricity upon demand. The round-trip storage cycle efficiency tosses of such systems are typically in the range of 25% and the difficulties in permitting, constructing and operating makes pumped hydro difficult to implement. It can take more than a decade to construct such a system. Unlike batteries, capacitors and flywheels a pumped hydro system is unlikely to be deployed for frequency regulation unless it is already in operation due to the limited output efficiency range of reversible turbines and their stow response times from shutdown to their peak efficiency flow rates. As such pumped hydro is generally only deployed for Regulation while actively charging or discharging and its economic efficiency as a provider of regulation service is limited by its overall system efficiency and the regional potential for time of use electricity price arbitrage.
An alternative form of potential energy storage technology may be achieved by constructing an electrified steel railway network which employs traction drive shuttle-trains with regenerative braking capability, operating on a closed low-friction automated steel rail network, to transport heavy masses between two storage yards at different elevations, converting electricity into potential energy and back into electric power as needed. In such a system when excess energy is available on the grid, the masses are transported uphill from a tower storage yard, drawing electricity from the grid to power the motors of shuttle-trains as they move the masses against the force of gravity to an upper storage yard; when the grid requires energy to meet periods of high demand, the process may be reversed, the shuttle-trains return the masses to the lower storage yard with their generators converting the potential energy of the masses back into electricity in a highly efficient process.
Therefore it is desirable to provide a fast responding, minimally polluting and cost effective ancillary services system for regulation up, regulation down, spinning, supplemental and replacement reserves, black start, and VAR support which may provide these services without a requirement to be actively providing bulk energy storage or supply at the time the ancillary service request is received.